This invention relates to an automatic clutch control apparatus used, for example, in controlling a wet-type multiple-disc clutch.
Automatic clutch control of a wet multiple-disc clutch is performed in such a manner that engine torque is not transmitted in a state where the vehicle is at rest and the accelerator pedal is not depressed. When the accelerator is in the depressed state, however, control is so effected as to transmit a torque commensurate with the engine rpm that prevails at such time.
FIG. 9 is a flowchart illustrating this conventional method of clutch control. If the shift position is the reverse, drive or low position (i.e. R, D or L, as indicated at a in the flowchart) and, moreover, the accelerator pedal is not being depressed (i.e. the accelerator is not ON, as indicated at (b), then a minimum value of solenoid current I.sub.s is outputted (c) by a control unit for providing a minimum clutch pressure P.sub.c that will turn off the clutch so that a transfer torque is not produced. If the accelerator pedal is being depressed (i.e. the accelerator is ON, as indicated at (d), on the other hand, the required value of clutch pressure P.sub.c [P.sub.c =f(N.sub.e,d)] is calculated at step f in accordance with the prevailing engine rotational speed N.sub.e (sensed at step e) and the amount of d of accelerator pedal depression. The required value of solenoid current I.sub.s is then calculated in the control unit at step g and outputted by the unit at step h. Next, the clutch input rotational speed N.sub.o and output rotational speed N.sub.ds are sensed by suitable sensor and a clutch engagement ratio C.sub.e (=N.sub.ds /N.sub.o) is calculated in the unit at step i. If the clutch engagement ratio C.sub.e is equal to or greater than 0.95 (meaning that synchronization has been attained), indicated at j in the flowchart, then the maximum value of solenoid current I.sub.s that will bring the clutch pressure to maximum (i.e. line pressure) is outputted at step k. If C.sub.e is less than 0.95 (i.e., synchronized), detection of engine rpm, calculation of P.sub.c [=f(N.sub.e,d)], calculation of I.sub.s (step g), outputting of I.sub.s, calculation of C.sub.e and the decision step C.sub.e .gtoreq.0.95 are repeated (l), providing the shift position is still R, D or L and the accelerator is ON.
If the accelerator is OFF (m) and the vehicle velocity is less than a set value (n) when the solenoid current I.sub.s is maximum, the solenoid current I.sub.s is changed over at step c to the minimum value of solenoid current I.sub.s, which turns off the clutch so that a transfer torque is not generated.
When the accelerator is switched from the OFF (m) to the ON state at such time that the outputted value of solenoid current I.sub.s is minimum (c), this conventional arrangement for controlling the automatic clutch functions to increase the solenoid current I.sub.s to its maximum value through the abovementioned process a, d, e-k in order to increase the transfer torque of the clutch. Consequently, there is a time lag between depression of the accelerator pedal and transfer of the torque by the clutch. This means that if the vehicle is propelled forward from rest on an upgrade, for example, the vehicle will move backward until torque transfer begins. This is a significant problem in the prior-art arrangement described above.